The mechanism controlling the initiation, elongation rate, and termination of flagellar growth in the bi-flagellate alga Chlamydomonas is being approached in the following ways: (1) Temperature sensitive mutants defective in flagellar development are being isolated and the defects analyzed by in vivo complementation analysis and biochemical procedures. (2) The role of flagellar precursor pool in controlling the initiation and rate of flagellar protein synthesis in the cytoplasm of Chlamydomonas is being investigated by use of in vivo single and double labeling procedures, coupled with the use of inhibitors of flagellar assembly. In addition, methods for increasing the flagellar precursor pool size in the cytoplasm are being used to determine the effect of pool size on flagellar protein synthesis. (3) The growth zone of the outer doublet and central flagellar microtubules is being investigated by use of mutants which lack the central tubules but can be induced to make them by fusion of the mutant with a wild-type cell. (4) Attempts are being made to assemble flagellar tubulin into microtubules in vitro. (5) The binding site(s) for dynein on the A and B tubules of outer doublet is being analyzed by use of flagella reactivation procedures, reversible protein cross linkers, and two-dimensional gel electrophoresis. BIBLIOGRAPHIC REFERENCES: Sloboda, R.D., Dentler, W.L., Bloodgood, R.A., Telzer, B.R., Granett, S., and J.L. Rosenbaum. 1976. Microtubule-Associated-Proteins (MAPs) and the Assembly of Microtubules In Vitro. Cold Spring Harbor Conference on Cell Motility, Edited by R. Goldman, T. Pollard & J. Rosenbaum. September, 1976 (In Press). Bloodgood, R.A. and Joel L. Rosenbaum. 1976. Initiation of brain tubulin assembly by a high molecular weight flagellar protein factor. Submitted to: J. Cell Biol. In Press.